The databases that store documents include a document database that stores indexes associated with images of the respective documents so as to improve the convenience of searching for a document or documents. Normally, each index holds the title, creator, date of update, and so forth, of a document with which the index is associated. The user can search information (index information) held in the indexes, and obtain desired document images based on index information found by the search. In recent years, some indexes hold, as index information, histories of updates, information on owners, information on access restrictions, etc. of documents.
An index is added when a copying machine having a printer function prints a document stored in a storage of the copying machine or a document stored in a personal computer connected to the copying machine via a network. Further, an index is also added when a document on a sheet medium is read using a scanner, and is stored as image data in the storage of the copying machine.
In the document database storing a large amount of documents, even when the user uses index information to search for a desired document, it is difficult to obtain the desired document in a single search operation by using the index information alone. In many cases, the user searches for the desired document as a target by repeatedly narrowing down the search, performing the search on a trial and error basis a plurality of times, and/or browsing each of documents found by the search one by one to see if it is the desired one.
Further, users sometimes wish to search for one or a plurality of documents found by a previous search as mentioned above, again from the database. In this case, it is necessary to perform complicated operations for narrowing down the search, as performed on the previous occasion, again, and hence the operations are very troublesome. To eliminate this inconvenience, Japanese Patent Laid-Open Publication No. H05-233703 proposes a technique which enables a user to add a new search keyword, for registration, to search keywords added to document image data. This enables the user to add a keyword or keywords of his own selection to document image data, whereby it is made easier for the user to find the desired document(s) again by a search using the keyword(s).
However, when the user searches the document database for a document or documents which he/she found by a previous search, again, the user often performs complicated operations for narrowing down the search, and/or repeatedly performing the search on a trial and error basis, as performed on the previous occasion, as mentioned above. On the other hand, in a case where the user desires to use a document found by a search on a previous occasion, there is a problem that a copy obtained by locally retrieving the document from the database cannot have updates made to the original document in the database reflected thereon, so that an old version of the document is used as it is.
Further, in a case where a document found by a search performed on a previous occasion is accessed again based on information on the search stored in the database, there is a problem that if a storage position of the document has been changed by an owner of the document, it is impossible to access the document based on the information stored in the database. As described above, when a document or documents is/are searched for again, there is a high possibility that it is required to perform complicated search operations, which impairs user's convenience.
Furthermore, in a case where the user adds a search keyword to document image data for additional registration, if another user happens to add the same search keyword to another document, it is impossible for the user to obtain the same result as obtained by the search performed on the previous occasion. This compels the user to give consideration to a search keyword to be added to a document such that the search keyword is the same as one added to other documents by another user. This reduces the degree of freedom of setting keywords, which also impairs user's convenience.